Epitaxy of hexagonal SiGe heterostructures
Wouter Peeters defended his PhD thesis at the Department of Applied Physics and Science 果冻传媒 on February 25.
![[Translate to English:]](https://assets.w3.tue.nl/w/fileadmin/_processed_/1/3/csm_Peeters_Wouter_APSE_PROM_AS_2592_aa95164ac6.jpg "[Translate to English:]")
The most stable crystal structure for silicon-germanium (SiGe) alloys is the cubic crystal structure, which are the foundation for electronic devices. While SiGe alloys are effective at what they do, there is one major drawback with these alloys 鈥� cubic SiGe alloys have an indirect bandgap. This means that they cannot emit light effectively. However, hexagonal SiGe alloys are known to emit light thanks to its direct bandgap. For his PhD research, Wouter Peeters explored ways of enhancing epitaxy 鈥� the growth of SiGe alloys in a hexagonal crystal structure.
Hexagonal silicon-germanium (hex-SiGe) alloys have recently been confirmed to have a direct bandgap, with light emission between 3.4 and 1.8 micrometer. An efficient light source in this wavelength range, compatible with CMOS technology, is highly sought-after.
Applications could be in sensing or data communication. Proposed optical interconnects for data communication promise a reduced energy consumption of computer chips, while simultaneously increasing their performance.
Promising material
Hex-SiGe alloys are a promising material system for light emission. However, the growth of SiGe in the metastable hexagonal crystal structure has certain challenges, which are discussed in Peeters鈥� thesis.
One of the major results of this thesis is the realization of quantum wells. These are structures in which electrons are localized in specifically designed layers, only a few nm in width.
Localize in quantum wells
Moreover, Peeters demonstrated that holes, i.e. missing electrons, localize in these quantum wells. These heterostructures where both charge carriers localize in the same layer are known as type-I quantum wells.
Similar quantum wells are already used in other material systems to increase the performance of lasers, and they may eventually be used to fabricate lasers of hex-SiGe as well.
In short, Peeters thesis addresses multiple aspects that are important in the epitaxy of hex-SiGe crystals and its heterostructures, and it paves the way toward light-emitting devices of hex-SiGe.
Title of PhD thesis: . Supervisors: Erik Bakkers, Marcel Verheijen, and Jos Haverkort.